HDTV (High Definition television) is called "second-generation TV", which is far superior to a conventional TV in image and audio qualities and realizes wide screen display. In recent years, with great advance in electronics technologies including digital techniques which are employed to digitize or compress video and audio data, the HDTV has been put into practical use. Accordingly, there has been an increasing need for techniques for transmitting and recording HDTV video, among which a method for performing image compression process to video data of a large capacity has been studied and developed to achieve high efficiency.
Video data is generally recorded in a digital format as follows. A video signal, i.e., an analog signal is first converted into digital image data comprising pixels, which is compressively coded to reduce amount of information, and then recorded and transmitted. In this case, DCT (Discrete Cosine Transform) which plays an important role in image compression process is employed. The DCT process is performed for pixel blocks each comprising (8.times.8) pixels (8 pixels in the horizontal direction.times.8 lines aligned in the vertical direction), and for macroblocks each composed of plural pixel blocks. Therefore, prior to DCT process, blocking process is performed to generate these blocks. For the case of performing blocking to an HDTV video signal, the following conversion process is performed.
The recording method for the HDTV signal is described in detail in IEC-61834 as an international standard of digital VTR. Hereinafter, a description will be given of a prior art HDTV signal processing techniques according to an 1125/60 system according to this recording method with reference to FIGS. 4 and 5(a)-5(d). FIGS. 4 and 5(a)-5(d) show block dividing process and block arrangement process according to the prior art HDTV signal processing technique.
FIG. 4 shows a target block to be compressively coded according to the prior art. In general, a moving image such as the HDTV video is represented by continuous motion of an image comprising numerous frames, and digital image data corresponding to one frame is decomposed into digital video signals Y, CR, and CB, which are hereinafter referred to as "Y", "CR", and "CB", respectively. The "Y", i.e., a luminance signal has a sampling frequency of 40.5 MHz, and one image thereof comprises (1008.times.1024) pixels (1008 pixels in the horizontal direction.times.1024 lines aligned in the vertical direction). The "CB" and "CR", i.e., chrominance signals, respectively have a sampling frequency of 13.5 MHz and one image of each of them comprises (336.times.512) pixels (336 pixels in the horizontal direction.times.512 lines aligned in the vertical direction), since every other lines thereof are reduced.
As described above, it is required that the digital video signal be divided into pixel blocks prior to DCT process. The "Y", "CR" and "CB" are respectively divided into pixel blocks each comprising (8.times.8) pixels. The pixel blocks to be subjected to DCT process are called "DCT blocks". In compressive coding process, a plurality of DCT blocks are generally handled as a macroblock. Referring to FIG. 4, there are shown 6 DCT blocks (DCT 0-5) corresponding to an image comprising (24.times.16) pixels in "Y", a DCT block (DCT 6) comprising (8.times.8) pixels in "CR", and a DCT block (DCT 7) comprising (8.times.8) pixels in "CB". These 8 blocks are handled as a macroblock. Arrangement changing process mentioned later is performed for each macroblock.
FIG. 5 shows arrangement of blocks and arrangement changing process in video signal processing according to a prior art.
According to arrangement of macroblocks generated by block dividing process, as shown in FIG. 5(a), upper and lower regions in one image are divided into blocks Ai (i=0-19), and a central region except the upper and lower regions are divided into blocks Ci (i=1-5). The blocks Ai (i=0, 1-7, 10, 11-17) are each composed of (9.times.1) macroblocks, and the blocks Ai (i=8, 9, 18, 19) are each composed of (6.times.1) macroblocks. The blocks Ci (i=1-4) are each composed of (9.times.60) macroblocks, and the block C5 is composed of (6.times.60) macroblocks. Thus, in a 1125/60 system, it is possible to divide one frame comprising (1008.times.1024) pixels into (42.times.64) macroblocks.
Then, arrangement of so divided macroblocks in one frame is changed as follows, for compressive coding process. As shown in FIG. 5(c), the blocks Ai (i=0, 1-7, 10, 11-17) each composed of (9.times.1) macroblocks are changed into blocks Bi (i=0, 1-7, 10, 11-17) each composed of (3.times.3) macroblocks. In addition, as shown in FIG. 5(d), the blocks Ai (i=8, 9, 18, 19) each composed of (6.times.1) macroblocks are changed into blocks Bi (i=8, 9, 18, 19) each composed of (3.times.3) macroblocks. Sine the macroblocks which belong to the blocks Ai (i=8, 9, 18, 19) are each configured in (6.times.1) arrangement, 3 dummy macroblocks are used as 3 macroblocks represented by oblique lines in FIG. 5 (d) This changing proces allows the blocks Bi (i=0-19) to be arranged at the right of C5, as shown in FIG. 5(b).
As a result of this rearrangement, the frame composed of (42.times.64) macroblocks becomes a frame composed of (45.times.60) macroblocks. Then, according to the arrangement of macroblocks of one image shown in FIG. 5(b), compressive coding including DCT process is performed, and the resulting coded data is recorded in a recording medium such as a magnetic tape.
Thus, in the prior art video signal processing, since it is necessary to divide the video signal into pixel blocks each comprising (8.times.8) pixels to be subjected to DCT process, and further divide the pixel blocks into macroblocks each comprising (24.times.16) pixels, the number of the lines aligned Din the vertical direction must be an integer multiple of 16. Although it is possible to divide the image comprising 1024 lines aligned in the vertical direction because the above condition is satisfied, it is impossible to divide an image comprising 1080 lines aligned in the vertical direction illustrated in SMPTE 274M according to an SMPTE standard because it is not satisfied.
For this reason, use of the above recording method does not realize recording in the magnetic tape or the like. As a solution to this, a portion of image data is abandoned.
As concerns a video signal processing apparatus according to the prior art which is capable of processing without abandoning data, a video signal recording apparatus is disclosed in Japanese Published Patent Application No. Hei. 9-46628. The recording apparatus includes an additional video area encoder for coding extra data, and records data in auxiliary video data areas in a recording medium, whereby the data is not abandoned.
However, to realize a recording apparatus which is capable of processing the image composed of 1080 lines aligned in the vertical direction, shown in the SMPTE274M based on a video signal processing apparatus according to the 1125/60 system, it is required that the apparatus be provided with an additional video area encoder, which causes cost-up and increases processing burden on the apparatus. In addition, the apparatus must have enough recording capacity, since there is a need for another area in which coded data processed by the additional video area encoder is recorded. Moreover, writing and reading process at recording and reproduction, is performed to different areas, which causes processing burden to be somewhat increased.